1. Field of Invention
This invention relates to a method and device of ion source generation and, in particular, the method and device can enhance the implanting efficiency of a shallow ion implantation.
2. Background of the Related Art
As shown in FIG. 1, an ion implanter uses a filament 100 to ionize the atoms and/or atom clusters to form ions and/or ion clusters in source chamber 200. An electric field accelerates the ions/ion clusters to form an ion beam 610 and, after passing a mass spectrometer 400, the ions/ion clusters of the ion beam 610 are filtered to have a specific charge-mass ratio. And, then the ion beam 610 injects into the implantation chamber 500 after passing the channel 300.
A target base 510 and a Faraday cup 600 are configured in the implantation chamber 500, and a wafer 520 is settled on the target base 510. The ion beam 610 collides with the wafer 520 with a specific collision depth, which proportionally depends on the kinetic energy of the ions/ion cluster of the ion beam 610. The implanting efficiency proportionally depends on the current of the ion beam 610, and an ion beam current detector 700, which electrically couples with the Faraday cup 600, can detect the current. The current detector 700 can be implemented by an ampere meter.
An ion cluster will distribute averagely the energy to each ion of the ion cluster, so the ion implanting energy should be reduced to be suitable for a shallow ion implantation.
FIG. 2 shows the curves of the temperature T and the ion beam current I, which vary with time t, where T is the shell temperature of the source chamber 200 and I is the current of ion beam 610 detected by the ion beam current detector 700. As shown in FIG. 2, from t=0, the time of lighting up the filament 100, to t=t1, ion beam current I increases and approaches to the maximum. In the meanwhile, temperature T increases and approaches a minimum threshold temperature Tm. T increases continuously with time, till time t=t2, and the ion beam current I surpasses the maximum ion beam current value and begins to decrease to a minimum threshold ion beam current Im and keep decreasing to be less than Im.
It is very important to keep a high ratio ion cluster for obtaining a high ion beam current, and a skill is proposed in this invention.